I'm assuming you didn't see any eggs? If so she was nesting. If not it could be a test nest. She could be hiding from the male if he is over exerting himself in courtship, yes males of similar but different species will court females. There is a male eastern painted at my businees partner's place of employment that totally ignores the female of his species in pursuit of a considerably larger female RES. There is in the same enclosure a male RES that court both the female of his species & a female N.A. wood turtle. Or it could be hiding from a presumed aivian predator. There are other possible reasons but those are the main 3.